Blender is only using one tile and only on CPU
Switch on GPU compute in the task manager. That will show you something else ;-) GPU compute is different than realtime rendering to task manager. It shows 97% to me while GPU 3D is barely working.

Go to GPU click on one of the sub diagrams like copy and select compute_0 or 1 or whatever yours is called.

be aware that you need something like 1080 before it is faster than a modern day cpu with 4-8 cores.